Japan's Tsunami History Shows What's in Store

Sept. 19, 2008 -- Newly discovered tsunami deposits suggest the Japanese coastline was hammered by a series of massive waves thousands of years ago. The finding adds to growing evidence that the region is regularly pounded by killer waves, and could help in planning for future inundations.

The northern Japanese island of Hokkaido is nestled up against the Kuril-Kamchatka trench, a place where the Pacific tectonic plate dives beneath the Eurasian plate, and home to terrible earthquakes in excess of magnitude 8.0.

Now Wesley Nutter and a team of researchers say nine waves, each at least 33 feet high, battered the coastline before the dawn of civilization on the island.

"In recorded history, tsunamis have hit the Hokkaido coast over and over again," Wesley Nutter of Earlham College in Indiana said. "But something of that size has never been recorded here."

Nutter and a team of researchers dug down into the sediments of a saltwater marsh on the island looking for signs of past tsunamis. Team member Kazuomi Hirakawa of Hokkaido University had first noticed a series of sand deposits several years ago there that had no business in a marsh mostly made of peat.

Tracing the sand deposits away from the coast, the team found they extend up to more than a mile inland and get thinner further from the sea.